1. Field of the Invention
The present invention relates generally to a manufacturing process for a semiconductor device. Particularly, the invention relates to a method of doping nitrogen atoms into a diamond semiconductor layer.
2. Description of the Related Art
Artificial diamond material manufactured at substantially low pressure for industrial use has been in use for some time. Recently, under vacuum pressure conditions it has been possible for form a layer of diamond material for use in semiconductor devices.
Compared to silicon, diamond has a higher carrier capacity and much faster transmission characteristics. Further, diamond exhibits a bandgap of 5.5 eV and may operate at much higher temperatures than silicon (i.e. 70.degree. C.). In addition, irradiation strength is high, therefore soft error due to .alpha. ray emission as experienced in LSI devices etc., is minimized. According to this, diamond is a preferable material for device required to operate in space (satellites, rockets, etc.), nuclear reactors and other harsh operating environments.
However, among the problems encountered in relation to use of diamond material as a semiconductor layer are that a low cost processing method has not been introduced, n type doping of a diamond conductive layer cannot be carried out and technique for etching processing of complex circuits is not available.
The problem of effecting n type doping by using nitrogen into the diamond semiconductor material has been among the most important factors to be realized to implement greater use of such material in semiconductor devices.
At this, when diamond is used as a material for semiconductor devices, doping efficiency may be extremely low. If a p type doping, that is to boron doping at 1000 ppm, a carrier density of only 10E16 cm.sup.-3 is obtained. Further, in n type doping hydrogen and carbon are highly present in the diamond material as compared with silicon or the like, and the particle radius of such components are quite small. Consequently, processes used for silicon as applied to diamond material may not use phosphorous. In processing using nitrogen, the particle radius thereof is very close to carbon. However, using nitrogen the problems as set forth below are encountered.
Nitrogen has a high degree of electron resistance, that is, electron energy of 1.7 eV is required. At room temperature, an extremely small number of electrons result and no motion is produced in the crystal, and an effective device will not result. Moreover, if nitrogen is used as a dopant, destruction of the crystal structure will result.
Thus it has been required to provide a technique for n doping of diamond material without destruction of the crystal structure.